Caprolactam, which is an organic compound, is a lactam of 6-aminohexanoic acid (ε-aminohexanoic acid, 6-aminocaproic acid). Unlike other compounds, caprolactam can be considered as a cyclic amide of caproic acid. One use of caprolactam is as a monomer in the production of nylon 6. Base materials that are most widely used in the production of caprolactam are aromatic compounds such as benzene, phenol, toluene, etc. Caprolactam is ultimately synthesized via the Beckmann rearrangement using sulfur catalysts by preparing oxime compounds via oximation, which drives a reaction of cyclohexanone with hydroxylamine obtained from the base materials of the aromatic compounds. When caprolactam is synthesized via such process, it is difficult to avoid formation of ammonium sulfate as a byproduct. In the production of caprolactam, the yield of caprolactam decreases as more ammonium sulfate is produced, and therefore, caprolactam can be obtained in high yield only if the formation of ammonium sulfate is suppressed.
Recent development trends for production techniques of caprolactam are divided into developing processes for reducing or eliminating the formation of ammonium sulfate or developing alternative base materials therefor. One example of the former development includes a caprolactam production facility recently developed by Sumitomo Chemical, Japan. This involves the Beckmann rearrangement in a gas phase using fluid bed gas-phase zeolite-catalysts and an ammoximation reaction using hydrogen peroxide catalysts (Enichem). Also, the base materials developed as alternatives for caprolactam include hexamethylene diamine (HMDA) and tetramethylene diamine (TMDA). HMDA can be produced from adiponitrile, propylene, and acrylonitrile. However, the process for HMDA production using adiponitrile can only be used by BASF, Solutia, Butachimie, and DuPont. Adiponitrile is produced by reacting butadiene with hydrogen cyanide. Butadiene may be used as a base material for adipic acid, which is a base material for nylon 4 and nylon 6. Most of the intermediates used in the production of nylon have their origins in butadiene, and such tendency is increasingly spreading.
As such, much more attention has been drawn to the production of these chemicals and materials from renewable non-food biomass via biorefinery as concerns about environmental problems and the availability of fossil resources increase. With the development of the biorefinery processes, microorganisms have been used as core biocatalysts capable of successfully producing chemicals, plastics, and fuels from renewable resources. However, non-manipulated natural microorganisms are not suitable for efficiently producing target products at the industrial level due to their reduced metabolism. Therefore, techniques that improve the metabolism of microorganisms have been actively studied to efficiently produce target products. Many studies are being conducted to solve the optimization of these microorganisms via systems metabolic engineering at the system level.
Accordingly, the present inventors have constructed a transformed microorganism capable of biosynthesizing 6-aminocaproic acid in the microorganism by expressing genes of enzymes used in the biosynthetic pathway of 6-aminocaproic acid, which is a precursor of caprolactam, to produce caprolactam.